1. Field of the Invention
The field of the invention relates to single use syringes and locking devices for locking the plunger assemblies of such syringes.
2. Brief Description of the Related Art
In the United States and throughout the world the multiple use of hypodermic syringe products that are intended for single use only is instrumental in drug abuse and more particularly in the transfer of diseases. Intravenous drug users who routinely share and reuse syringes are a high risk group with respect to the AIDS virus. Also, the effects of multiple use are a major concern in developing countries where repeated use of syringe products may be responsible for the spread of many diseases.
Many syringes have been made to remedy this problem. Some of these have required a specific act to destroy the syringe after use either by using a destructive device or providing a syringe assembly with frangible zones so that the syringe could be rendered inoperable by the application of force. Other syringes include structure which allows the destruction or defeating of the syringe function through a conscious act by the syringe user. Although many of these devices work quite well, they do require the specific intent of the user followed by the actual act to destroy or render the syringe inoperable. None of these devices is effective with a user having the specific intent to reuse the hypodermic syringe.
Single use hypodermic syringes that become inoperative or incapable of further use automatically without any additional act on the part of the user have been developed. One such syringe is disclosed in U.S. Pat. No. 4,961,728. The syringe disclosed in this patent includes a locking element positioned in the syringe barrel. The locking element includes proximally and outwardly facing barbs that engage the inner surface of the syringe barrel and an inwardly facing driving edge adapted to interact with the plunger rod to move the locking element along the barrel as the stopper is advanced. The plunger rod includes a ledge positioned at a distance from the proximal side of a support wall that approximates the length of the locking element. The driving edge of the locking element engages the ledge, thereby ensuring that the locking element moves distally with the plunger rod and stopper. A syringe including a similar locking element is disclosed in U.S. Pat. No. 5,989,219.
U.S. Pat. Nos. 5,021,047, 5,062,833 and 5,562,623 disclose single use syringes having plunger rods that have teeth or ridges and locking elements that engage the teeth or ridges. The locking elements of these syringes also include outwardly extending teeth or prongs that engage the inside surface of the syringe barrel. The plunger rods of these syringes can be retracted to draw fluid into the syringe barrel while the locking elements remain stationary. Distal movement of the plunger rods causes the fluid to be expelled, the locking elements moving distally with the plunger rods with the intention of preventing further plunger rod retraction.
Although the prior art provides syringes having locking elements that will automatically lock the syringe barrel and plunger rod to help prevent re-use, there is still a need for additional features that will cause the destruction of the syringe""s functionality if excessive force is used to withdraw the plunger rod after injecting medication.
A locking element for locking a syringe plunger rod having a stopper, with respect to a syringe barrel and for rendering a stopper unusable is provided by the invention. The locking element includes a body portion having distal and proximal end portions. First and second means are provided on the body portion for engaging a plunger rod and syringe barrel, respectively, such that the locking element can slide distally, but not proximally, with respect to the syringe barrel. One or more cutters are attached to, and preferably integral with the distal end portion are provided for cutting the stopper if excessive force is applied to the plunger rod. The cutter may be formed by a cutting edge.
The invention further relates to a syringe assembly including a locking element capable of locking a plunger rod with respect to a syringe barrel and rendering a stopper unusable. The assembly includes a syringe barrel, a plunger rod, a locking element and a cutter. The syringe barrel includes an inside surface defining a chamber, an open end, and a distal end. The plunger rod assembly includes an elongate body portion and a stopper. The locking element is slidably-positioned within the chamber of the syringe barrel, engaging the inside surface thereof such that the locking element is substantially immovable in the direction of the open end of the syringe. It is also engageable with the plunger rod assembly such that the plunger rod assembly and locking element can be moved distally together toward the distal end of the syringe barrel. In a preferred embodiment, the plunger rod assembly can initially be moved proximally with respect to the locking element to aspirate fluid into the syringe barrel. A cutter is connected to the locking element and is engageable with the stopper. The cutter is capable of cutting the stopper upon attempted withdrawal of the plunger rod assembly from the syringe barrel.
A further embodiment of a locking element for a single use syringe having a plunger rod with a stopper is also provided. The locking element includes a distal portion and a proximal portion. The distal portion includes a generally V-shaped body comprising first and second walls connected along a longitudinal axis. A first leg extends proximally from the first wall of the body. A second leg extends proximally from the second wall of the body, and is separated from the first leg by a gap. Each leg includes one or more barbs. A cutting member is provided on a distal portion of the locking element. One or more barbs may also be provided on the distal portion of the locking element. This portion preferably further includes a pair of distally extending legs. The barbs are preferably integral with the distal ends of the distally extending legs.
A further single use syringe assembly in accordance with the invention includes a barrel having an inside surface defining a chamber for retaining fluid. The barrel has an open proximal end and a distal end having a passageway in communication with the chamber. A plunger rod assembly is provided for use in conjunction with the barrel. The plunger rod assembly includes an elongate body portion having a proximal end, a distal end, and a stopper mounted to the elongate body portion proximate the distal end. The stopper is slidably positioned in substantially fluid tight engagement with the inside surface of the barrel. The elongate body portion of the plunger rod assembly extends outwardly from the open proximal end of the barrel. It includes at least one elongate recess. A plurality of steps or teeth are provided within the recess. A locking element is positioned within the barrel. One or more proximally facing barbs extend from the locking element. The barbs engage the inside surface of the barrel for substantially preventing the locking element from moving proximally with respect to the barrel. The locking element also engages the elongate body portion of the plunger rod assembly such that the locking element is movable towards the distal end of the barrel as the plunger rod assembly is advanced. Each tooth defines a distally facing surface that is engageable by a proximal edge of the locking element. A cutting member is provided on the distal end of the locking element.
A single use syringe assembly is further provided that includes a barrel having an inside surface defining a chamber for retaining fluid, a plunger rod assembly, and a locking element. The plunger rod assembly includes an elongate body portion having a proximal end, a distal end and a stopper mounted to the elongate body portion. The stopper is slidably positioned in substantially fluid tight engagement with the inside surface of the barrel. The locking element is positioned within the barrel. It includes a generally V-shaped body comprising first and second walls connected along a longitudinal axis. A first leg extends proximally from the first wall and a second leg extends proximally from the second wall. A first barb extends from the first leg of the locking element while a second barb extends from the second leg thereof. It will be appreciated that one or more barbs may extend from the legs of the locking element. Each leg includes an end portion engageable with the body portion of the plunger rod assembly. The locking element preferably includes proximally facing barbs near the distal end of the V-shaped body, preferably extending from a pair of legs integral with the V-shaped body. The locking element can accordingly be moved distally with the plunger rod assembly along the syringe barrel. The barbs substantially prevent the locking element from moving proximally therein. A cutting member is provided at the distal end of the V-shaped body for cutting the stopper.